Means for eliminating fading



m 31933 E. w. ALEXANDERSQN 19$53 21 MEANS FOR ELIMINATING FADING FiledNov. 15, 1927 inventor:

Patented Apr. 12, 1932 ERNST F. W. ALEXANDERSON, OF SCHENECTADY, NEWYORK, ASSIGNOR TO GENERAL ELECTRIC. COMPANY, A CORPORATION OF YORK MEANSFOR ELIMINATING FADING Application filed November 15, 1927. Serial no.233,508.

My present invention relates to radio signaling systems employ-ing shortwave lengths and more particularly to a method and means foreliminating. fading in such systems.

As a result of observations it has been shown, when two receivers aremade to respond, one to waves having a predominant polarization in acertain plane and the other to waves having a predominant polarizationin a different plane, that the periods of fading do not occursimultaneously in the different receivers but rather that they morefrequently occur alternately. This I attribute to changes in the planeof polarization of the received wave. This seems to be borne out by thefact that it has been shown that a'wave emitted by a horizontal loop maypro-- duce a response in receivers situated at different distances-fromthe antenna indicating a continuously twisting planeof polarizationtogether-with alternate points of plane and circular polarization andintermediate points of elliptical polarization.

which have been variously'observed seem to indicate that the conditionofpolarization of the wave as it passes through space is continuallychanging and I have been led to believe that the phenomenon of fading isa result of this shifting of the condition of polarization of thetransmitted waves. I have accordingly designed a system in which radiosignaling may be effected by means of waves having a circular orelliptical polarization,

or a rapidly changing plane of polarization.

ployed.

At the receiving station I provide a simi' set up in both of theseantennae.

These phenomena together with others lar system of antennae theseantennae being disposed substantially at right angles to each other andeach being adapted to respond to waves having a predominant polarizationin ceiving apparatus and also if there be no fading in either plane,'thetransmitted circularly polarized waves or waves having a rapidlychanging plane of polarization will effect both of the receivingantennae andthe re-' ceivmg apparatus will respond to currents The novelfeatures which I believe to 'be characteristic of my inventionwill beset forth with particularity in y the appended claims. My inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the accompany-ing drawings in which Figs. 1 and 3 representparticular formsof apparatus which I may employ at the transmitter, andFigs. 2 and/1 represent apparatus which I may employ at the receiver.

Referring to Fig. 1 of the drawings, 1 represents an antenna which initself is adapted to transmit horizontally polarized waves. 'Thisantenna may be constructedin a manner which has been fully set forth inmy copending application, Serial No. 29,210,; filed May 9, 1925, Radiosignalling system and comprises in the-illustration a simple horizontaldoublet. 2 represents a similar-vertical antenna adapted to transmitvertically polarizedwaves. These antennae may be of any suitableconstruction but for purposes of illustration are shown as comprising asingle conductor havin a-length equal to substantially half of t e wavelength of the wave to be radiated and which are locatedrespectively inthe horizontal and vert1cal- Y planes.

rents to the detector 12 causi'n a response in ceeding interval Both oftheseantennae are excited with high frequency currents which aresupplied thereto at substantially the midpoint thereof, through feedertively, cuit of a high frequency transmitter 5. This transmitter isadapted to supply .to its associated antenna currents having a desiredfrequency through suitable phase adjusting means 6 and 7 which arerepresented as series lines 3 and 4 respecconnected capacitance 1n theline 3 and 111- ductance in the line 4- The phase relations between thecurrents in the twoantennae may be adjusted and maintained as desired bythis variable inductance and capacity.

In Fig. 2 I have shown antennae 9 and 10 both of which may beconstructed similarly with the antennae l and 2 of Fig. 1, theseantennae being disposed at right angles. to each other, one in ahorizontal plane and the other in a vertical plane. The antenna 9 isadapted to respond to oscillations in the horizontal lane and to supplycurrents so received t rough a transformer 11 to a suitable detector 12.Likewise the antenna 10 is adapted to respond to oscillations in thevertical plane and to supply currents so received through a transformer13 to a suitable detector 14. 15 represents any suitable receivingapparatus which may be associated with the output circuits of both ofthese detectors and which may respond to either of them independently ofthe other, or to both.

With the apparatus as thus shown and described, if the antenna 2 beexcited with currents which are displaced in phase by 90 degrees withrespect to the currents with which antenna 1 is excited, waves will betransmitted which have a circular or elliptical polarization. If itshould occur at a certain time interval that fading be pronounced withwaves having a vertical polarization horizontally polarized waves maystill reach. the receiving apparatus. To these antenna 9 will respondsupplying high frequency ourthe receiving apparatus 15. uring asucfading may be pronounced with waves having a polarization in thehorizontal plane. During this time vertically polarized waves may stillreach the receiving apparatus. To these antenna 10. will respondsupplying high frequency currents to the detector 14 and producing aresponse in the indicating apparatus. Ifno fading occurs in either planethen the antenna 10 will respond to oscillations in the vertical planeand the antenna 9 will respond to oscillations in the horizontal planeand both detectors 12 and 14 will supply signalling currents to thereceiving apparatus 15.

In Fig. 3 I have shown another form of transmitting apparatus which maybe employed as a part of my invention including antenna 1 and 2 of aformmore fully set which are connected in the output cirforth and describedin Patent No. 1,775,826

vertical plane. Each of these sections have a length equal to one halfof the length of the wave which is to be radiated and they arepreferably arranged in a zigzag or staircase formation upon oppositesides of asupporting member, such-as a tower 18,- from which they aresuspended by means of additional members 19 and 20. The generalarrangement of the antennae, as shown, comprises that of a triangle.Theantenna may be supplied with high frequency currents as set forth inconnection with Fig; 1 in which case a circular polarized wave will beprojected in a direction broad side to the plane of the antenna. By wayof illustrating a further means for energizing the antennae 1 and 2 ofFig. 3 transmitters 21 and 22 are illustrated each of these beingassociated with the antennae 1' and 2 ers connected in the lines 3 and 4respectively. These transmitters are adapted to operate at the samefrequency and with a desired phase relation between their outputcurrents. The synchronism and phase relation of. the two transmittersmay be controlled by any suitable master control device 23. This controldevice may include a crystal of ordinary type which may be utilizedtocontrol the frequency of the transmitters 21 and 22, or

may include any suitable oscillation genand 22 currents which may beamplified and employed to excite the antennae. It will also includesuitable phase adjusting means such, for example, as that shown at 6 and7 in Fig. 1 for securing a .proper phase relation between the antennaecurrents. ters may be controlled in accordance with desired signals byany suitable device such as a telegraphic key 8. v v

In Fig. 4 I have shown a receiving system employing a similar type ofantennae. Each of these antennae will in itself produce a maximumresponse in the receiver 15 when waves are received having apolarization in a plane at right angles to the direction of the antennaas is indicated by the arrows 24 and 25 but either antenna will alsorespond to waves having either a vertical or horizontal polarizati'bn.Thus, for example, if waves having a horizontal p 'larization arereceived the horizontal members of both antennae will operate in phaseto supply currents to the receiving device, whereas no response will beproduced by the vertical members. Likewise if -vertical1y polarizedwaves are received the vertical members will respond in by thehorizontal members.

through suitable transform- I The antenna The transmitshown in thisfigure will, of course, be arranged in a plane at right angles to thedirection of propagation of the received wave.

An alternative method of operation is possible with an arrangement ofantenna such as that shown in any of the figures. For example, it may bedesirable instead of effecting communication by means of circularlypolarized waves to utilize waves having plane polarization which may bechanged as desired. This mayvbe'effected if desired, by

switching means which may be utilized to alternately connect each of theantenna of any of the figures to the associated high frequencyapparatus. This is true with respect to the receiver as well as thetransmitter. The means whereby the plane of polarization may be changedis particularly simple in the arrangement shown in Fig. '3 since theonly additional equipment necessary is a reversing switch 26 connectedpreferably in the leads extending from the master control device 23 toone of the transmitters whereby the current in the antenna 2 may bereversed in phase. A similar" result may be had by connecting thereversingswitch in the antenna leads 4. If the phase controlling device23 is so adjusted that both of the antennaa are excited in phase thenthe currents in all of, the horizontal members will be in phase and willcooperate to project a wave having a horizontal plane of polarization,whereas the vertical members of the antenna 2will be opposed to thevertical members of the antenna 1 with the result that the effects ofthe vertical members in a direction at right angles to the plane of theantenna will be neutralized. If now the currents in the an:

tenna 2 bev reversed in phase then the curpose those of the horizontalmembers of theantenna 2 and the effects of all of the horizontal memberswill be neutralized. Thus by the mere utilization of a reversing switch26 in the manner'described this result may be effected and eitherhorizontally or vertically polarized waves may be transmitted as desireddepending upon the nature of the re sponse which is had at the receiver15. This may be particularly advantageous where it of the antennae withrespect to the other will be rapidly reversed, and consequently a theplane of polarization will be rapidly changed from one plane to another.In this way the elimination of fading may be ex:

pected for the reasons pointed out in connection with the transmissionof circularly polarlzed waves. Where more rapid reversals are desiredelectrical means may be employed for effecting aphase modulation of thecurrents in either one or both of the antennae, it will, of course, beunderstood that I do not wish to be limited thereto, since the antennaemay be disposed at any angle with respect to each other, the phaserelations of the currents in the two being accordingly adjusted toproduce a circular polarization. Likewise while I have shown only a pairof antennae it will, of course, be understood that any number of thesemay be used, these beingarran ed at diverse angles to each other and atdi erent locations as is desired. This may be particularly advantageousin connection with the receiving apparatus. I further wish it to beparticularly noted while I 1 have shown a partlcular type oftransmitting mechanism in connection with my invention that asubstantial reduction. of fading has been found when the waves have beentransmitted in the customary way and only the receiving mechanism hereindisclosed has been employed; I therefore fully contemplate the use of myreceiving apparatus independently. of any particular type oftransmitting equipment as well as in combination with the transv mittingequipment as herein set forth.

I have shown the detectors 12 and 1 1 as being adjustable as isindicated by the arrows which have been drawn therethrough. Byadjustment ofuthe volume of output of these detectors reception may behad in the plane in is found that the fading is of a particular whichstaticis a minimum For example if nature during certain hours of theday. Thus it may occur that during a certain period of the'day "fadingis pronounced inthe horizontal plane,'wherea's during a different periodof the day it is pronounced in a different plane. By means of the switch26 the plane maybe chosen which will produce a maximum response at thereceiver 15; If desired the reversing switch 26 may be driven by a bothantennae are responding to oscillations in their respective planes,whereas static is present only in, for example, the horizontal courselee-understood that I do not wish to be limited thereto, since manymodifications, both in the circuit arangement and in thefinstrumentalities employed, may be made without departing from thespirit and scope of my invention as set forth in the appended claims.

What I claim as new and desireto secure by Letters Patent of the UnitedStates is:

1. In combination, an antenna having a plurality of alternately arrangedmembers disposed in different planes, a second antenna having aplurality of members similarly arranged in planes parallel to said firstmen- .tioned planes, means including high frequency apparatus associatedwith both of said antennae whereby certain members of both of saidantennae cooperate in a certain plane and means whereby certain othermembers of both of saidantennae cooperate in a different plane.

2. An aerial system comprising a pair of antennae, each of said antennaecomprising a plurality of sections, means for supplying high frequencycurrent to said antennae, the

arrangement of said antennae being such that certain sections of bothantennae cooperate to project a wave having a predominant polarizationin a certain plane and means for causing certain other sections of saidantennae to cooperate to project a wave having a predominantpolarization in a different plane,

3. In combination, an antenna comprising a plurality of series connectedsections including alternately arranged sections separated byintermediate sections, the alternately arranged sections of said antennabeing in parallel planes and extending in opposite directions from theintermediate sections thereof in zigzag formation, a second similarantenna having sections arranged in parallel relation with said firstantenna, said two antennae being arranged in a common plane and in ageneral triangular formation in said plane, means for supplying currentshaving a certain phase relation to said an-- tennae and means forreversing the phase relation-between said currents.

4. In combination, an aerial conductor arranged to radiate waves havingpolarization in both the vertical and horizontal planes,

and means selectively to neutralize the radiation from saidaerialconductor which is polarized in either of said lanes wherebradiation may be produc having pre ominant polarization in a selectedone of said planes.

5. In combination, a plurality of aerial conductors, each of saidconductors being arranged to radiate waves having polarization in eachof two planes at substantially right angles to each other, said antennaebeing so arranged with respect to each other that the radiation from thedifferent conductors polarized in one of said planes cooperate with eachother whereas the radiation from the different conductors polarized inthe other plane oppose, and means to cause the radiation from thedifferent conductors polarized in said one plane to oppose and theradiation from the difierent conductors polarized in said other plane tocooperate.

6. In combination, a plurality of aerial conductors, said aerialconductors being arranged to cooperate with respect to waves polarizedin a certain plane and to oppose each other with respect to wavespolarized in a different plane, and means for causing said conductors tooppose each other with respect to waves polarized in said certain planeand to cooperate with respect to waves polarized in said differentplane.

In witness whereof, I have hereunto set my hand this 14th day ofNovember, 1927. ERNST F. W. ALEXANDERSON.

